Actual evapotranspiration is one of the strongest predictors of decomposition on a global scale (Aerts, 1997), although its explanatory power is quite weak (r2 = 0.14). Regionally, the relationship between rainfall and decomposition appears even weaker. Using elevation gradient studies within tropical forests, Silver (1998) found no predictive relationship between rainfall and decomposition rates. A 50% reduction in precipitation reaching the forest floor had no effect on litter decomposition rates in a partial throughfall exclusion experiment in a moist forest in Amazonia (Nepstad et al., 2002), and dry-season irrigation resulted in only a small increase in decomposition rates of the forest floor in a moist forest in Panama (Wieder and Wright, 1995). In Hawaii, leaves decayed faster in moist forests than in wet forests (Schuur, 2001), but a common substrate showed a weaker trend, suggesting an important interaction of plant characteristics with climate or site conditions. Given this, the direct effects of either an increase or a decrease in mean annual precipitation on decomposition would probably be quite small. There are, however, indirect effects of climate change that might significantly affect the rate of both decomposition and mineralization of essential nutrients. In tropical sites, litter chemistry and in particular C : P, lignin : P, C: N, and lignin: N ratios are often inversely related to decomposition rates (Ostertag and Hobbie, 1999; Hobbie and Vitousek, 2000). As discussed above, both decreased rainfall and/or elevated atmospheric C02 might lead to increased C : nutrient ratios in litter. Significant immobilization of nutrients during the early stages of decomposition is commonly observed in tropical forest ecosystems (0stertag and Hobbie, 1999; McGroddy et al., 2004; but see Kitayama et al., 2004). Increased C: nutrient ratios in leaf litter could increase immobilization of nutrients in the microbial biomass during decomposition, could lower mineralization rates, and could reduce plant available nutrient pools.

Below-ground decomposition appears to be less sensitive to climate factors than above-ground litter, with tissue quality playing a key role in regulating the rate of decay (Silver and Miya, 2001). Matamala and Schlesinger (2000) found no effect of elevated C02 on root decomposition or tissue quality in a young temperate loblolly pine forest, though previous studies have found decreased root tissue N content under elevated C02 treatments (Crookshanks et al., 1998).

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  • Patricia Smith
    What affects decomposition rate in a rainforest?
    8 years ago

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